Efficiency of oocytes retrieval during a repeated series of transvaginal ultrasound-guided puncture of follicles in Simmental heifers

The article presents data on the efficiency of a repeated series of transvaginal ultrasound-guided recovery of oocytes (OPU) in donor heifers of the Simmental breed. Two series were performed — five OPU sessions with an intensity of once a week and a two-week rest period between series. During the repeated series of OPUS, 1.7 fewer follicles were visualized in donor heifers on average per session compared to the value of this indicator established in the first series (7.0 versus 5.3 follicles, p < 0.05). A decrease in the number of ultrasound-visible follicles during repeated series at the trend level was noted in all five OPU sessions. During the repeat series, 0.4 fewer oocyte-cumulus complexes (OCCs) were obtained from one donor on average per session (3.1 versus 2.7 OCCs). There were no differences in the quality of OCCs between the two OPU series: the proportion of OCCs suitable for further use was 67.0% and 63.5%, respectively, while in individual OPU sessions the differences between the series were multidirectional. Fertilization of oocytes and further in vitro cultivation showed a significantly higher degree of the first division — crushing during the 1st series of OPU (p < 0.05), however, these differences were leveled with further cultivation: the yield of blastocysts was, respectively, 23.6% and 21.7%. Considering the absence of significant differences in the quantitative characteristics of the obtained oocytes, as well as their developmental competencies in vitro, conducting a repeat series of OPU after a two-week rest period may be recommended for obtaining oocytes in donor heifers of the Simmental breed.